1. Field of the Invention
The present invention relates to route optimization by a mobile router of a mobile network, for example a mobile IP network (NEMO) or an Internet Protocol (IP) based mobile ad hoc network (MANET), and an access router providing an attachment point to a wide area network such as the Internet.
2. Description of the Related Art
Proposals have been made by Internet Engineering Task Force (IETF) groups for improved mobility support of Internet Protocol (IP) based mobile devices (e.g., laptops, IP phones, personal digital assistants, etc.) in an effort to provide continuous Internet Protocol (IP) based connectivity. The IETF has two working groups focusing on mobile networks, a Mobile Ad-hoc Networks (MANET) Working Group that is working to develop standardized MANET routing specification(s) for adoption by the IETF, and NEMO (mobile networks). NEMO uses Mobile IP (MIP) to provide connectivity between mobile networks and the infrastructure (e.g., the Internet). The key component in NEMO is a mobile router that handles MIP on behalf of the mobile networks that it serves.
A “Mobile IPv6” protocol is disclosed in an Internet Draft by Johnson et al., entitled “Mobility Support in IPv6”, available on the World Wide Web at the address: http://www.ietf.org/internet-drafts/draft-ietf-mobileip-ipv6-24.txt (the disclosure of which is incorporated in its entirety herein by reference). According to Johnson et al., the Mobile IPv6 protocol enables a mobile node to move from one link to another without changing the mobile node's IP address. In particular, the mobile node is assigned a “home address”. The “home address” is an IP address assigned to the mobile node within its home subnet prefix on its home link. While a mobile node is at home, packets addressed to its home address are routed to the mobile node's home link, using conventional Internet routing mechanisms.
The mobile node also is assigned a home agent for registering any care-of address used by the mobile node at its point of attachment to the Internet while the mobile node is away from its home link. A care-of address is an IP address associated with a mobile node that has the subnet prefix of a particular link away from its home link (i.e., a foreign link). A home agent is a router on a mobile node's home link with which the mobile node has registered its current care-of address. While the mobile node is away from its home link, the home agent intercepts packets on the home link destined to the mobile node's home address; the home agent encapsulates the packets, and tunnels the packets to the mobile node's registered care-of address.
The NEMO working group has extended the features of Mobile IPv6 (which to date have been limited to an IPv6 mobile node such as a wireless laptop) to a mobile network based on providing routing protocols that enable the mobile router to attach to an access router and establish route optimization for the mobile router and its associated mobile network. One example of proposed solutions for route optimization in a nested mobile network is disclosed in the Internet Draft by Thubert et al., “Taxonomy of Route Optimization models in the Nemo Context”, available on the IETF website at http://www.ietf.org/internet-drafts/draft-thubert-nemo-ro-taxonomy-02.txt and the disclosure of which is incorporated in its entirety herein by reference (referred to hereinafter as “Thubert-RO”). In particular, Thubert-RO notes that NEMO enables Mobile Networks by extending Mobile IP to support Mobile Routers; Thubert-RO describes how Route Optimization as described in the context of MIPv6 can to be adapted for NEMO to optimize traffic routing between nodes in a mobile network and their correspondent nodes.
Another example of a proposed solution for route optimization is disclosed in the Internet Draft by Thubert et al., “IPv6 Reverse Routing Header and its application to Mobile Networks” available on the IETF website at http://www.ietf.org/internet-drafts/draft-thubert-nemo-reverse-routing-header-04.txt and the disclosure of which is incorporated in its entirety herein by reference (referred to hereinafter as “Thubert-RRH”). Thubert-RRH discloses that Mobile IP can be extended to support mobile routers, and enable nested mobile networks, using a reverse routing header that eliminates the need for nested tunnels between mobile routers and their home agents, but rather enables use of a single tunnel between a mobile router and its associated home agent.
One particular aspect of the above proposals is that the mobile router communicates with its associated home agent to ensure reachability between the mobile router and the wide area packet switched network (e.g., the Internet). It may be desirable in certain cases to reduce the necessity for a mobile router to establish a tunnel with its associated home agent in order to have connectivity with the wide area packet switched network. For example, it may be desirable in certain cases that a mobile router can establish anonymous route connections without notifying the home agent of the source of the route connections. It also may be desirable in certain cases that a mobile router can establish multiple attachments with different access routers as the mobile router moves (i.e., “roams”) across the respective service of the access routers, without the necessity of notifying the home agent of each attachment, especially when the attachment may be for only a transient interval.
Other proposals attempt to minimize nesting of tunnels, as well as avoid a tunnel between a mobile router and its corresponding home agent, by adding prescribed operations to a top level mobile router of a mobile network. One example is described in the Internet Draft by Kang et al., “Route Optimization for Mobile Network by Using Bi-directional Between Home Agent and Top Level Mobile Router”, available on the World Wide Web at http://www.watersprings.org/pub/id/draft-hkang-nemo-ro-tlmr-00.txt and incorporated in its entirety herein by reference.
Another example of minimizing nesting of tunnels and avoiding a tunnel between a mobile router and its corresponding home agent involves use of a mobility anchor point (MAP). A variation of the Mobile IPv6 protocol is disclosed in an IETF Internet Draft by Soliman et al., “Hierarchical Mobile IPv6 mobility management (HMIPv6)” June 2003, available on the World Wide Web at http://www.ietf.org/internet-drafts/draft-ietf-mobileip-hmipv6-08.txt and incorporated in its entirety herein by reference. The Internet Draft by Soliman et al. discloses a Mobility Anchor Point (MAP) within an IPv6 network that implements HMIPv6 by assigning a regional care-of address to mobile nodes within its address realm. Mobile nodes may thus use on-link care-of addresses for communications within the address realm of the MAP, and the regional care-of address for lPv6 communications outside the MAP address realm. As such, the MAP serves as a local home agent.
Hence, a mobile node is always addressable by its “home address”: packets may be routed to the mobile node using this address regardless of the mobile node's current point of attachment to the Internet. The mobile node also may continue to communicate with other nodes (stationary or mobile) after moving to a new link. The movement of a mobile node away from its home link is thus transparent to transport and higher-layer protocols and applications. As apparent from the foregoing, however, Soliman et al. is limited to mobile nodes, and does not describe use of HMIP for a mobile router in a manner that could be applied to a mobile network served by the mobile router. However, route optimization has been described in the Internet Draft by Ohnishi et al., “HMlP based Route Optimization Method in a Mobile Network” available at the IETF website at http://www.ietf.org/internet-drafts/draft-ohnishi-nemo-ro-hmip-00.txt and the disclosure of which is incorporated in its entirety herein by reference.
Of particular interest is a proposal that describes using prefix delegation, such as Dynamic Host Configuration Protocol (DHCP): DHCP is described in Droms et al., “Dynamic Host Configuration Protocol for IPv6 (DHCPv6)”, published by the IETF as a Request for Comments (RFC) 3315 and available on the World Wide Web at http://www.ietf.org/rfc/rfc3315.txt (the disclosure of which is incorporated in its entirety herein by reference). Prefix delegation in DHCP is described in Troan et al., “IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6”, published by the IETF as RFC 3633 and available at the IETF website at http://www.ietf.org/rfc/rfc3633.txt (the disclosure of which is incorporated in its entirety herein by reference).
In particular, the Internet Draft by Lee et al., “Route Optimization for Mobile Nodes in Mobile Network based on Prefix Delegation”, available at the IETF website at http://www.ietf.org/internet-drafts/draft-leekj-nemo-ro-pd-02.txt (the disclosure of which is incorporated in its entirety herein by reference) discloses an access router that delegates a prefix to a top level mobile router.
FIGS. 1 and 2 are diagrams from the above-incorporated Internet Draft by Lee et al. FIG. 1 illustrates a network 10 having mobile routers 12a and 12b attached to their respective home agents 14a and 14b. The home agents 14a and 14b each provide a point of attachment in FIG. 1 between the respective mobile routers 12a and 12b and the Internet 16, enabling the mobile nodes 18 to communicate with a correspondent node 20. Each of the home agents 14a and 14b has a corresponding home address prefix: the home agent “HA-MR1” 14a has a home address prefix 22a of “1::”, and the home agent “HA-MR2” 14b has a home address prefix 22b of “2::”, according to the IPv6 addressing convention specified in RFC 3513, available on the Internet at http://www.ietf.org/rfc/rfc3513.txt (the disclosure of which is incorporated in its entirety herein by reference). Hence, the mobile routers “MR1” 12a and “MR2” 12b are assigned by their respective home agents 14a and 14b the mobile network prefixes 24a and 24b having respective values “1:1::” and “2:1::”. Consequently, the mobile routers 12a and 12b advertise their respective mobile network prefixes 24a and 24b to their respective attached nodes 18 and consequently form mobile networks 30a and 30b. FIG. 1 also illustrates an access router 26 having a corresponding local network 42, also referred to herein as a visited network, having a network prefix 28 with a value of “3::”.
FIG. 2 illustrates a revised network topology 10′ based on the movement of the mobile routers 12a and 12b from their respective home agents 14a and 14b and attachment with the access router 26. As shown in FIG. 2, each mobile router (e.g., 12a and 12b) has a home address (HoA) (e.g., 34a, 34b) based on its corresponding home address prefix (e.g., 22a, 22b): the home address 34a of the mobile router (MR1) 12a has a value of “1::1” within the address space of the home address prefix 22a “1::”, and the home address 34b of the mobile router (MR2) 12b has a value of “2::3” within the address space of the home address prefix 22b “2::”.
According to the Internet Draft by Lee et al., the mobile router 12a detects movement and obtains a delegated prefix (DP) 32a having a value of “3:1::” from the access router 26 according to a prefix delegation protocol such as DHCPv6. The detection of movement by the mobile router 12a is based on, for example, a detected loss of connectivity with the home agent 14a, detecting router advertisement messages from the access router 26, and attaching to the access router 26. In response to receiving the delegated prefix 32a, the mobile router 12a builds a care-of address (CoA) 36a within the network prefix 28, and performs a binding update with its home agent 14a to enable the home agent 14a to identify that the home address 34a of the mobile router 12a is reachable via the care-of address 36a. 
In response to assignment of the delegated prefix 32a, the mobile router 12a also outputs router advertisement messages that advertise the delegated prefix 32a, using a prescribed Delegated Prefix option. Note that the mobile router 12a also outputs router advertisement messages that advertise its mobile network prefix 24a. The second mobile router (MR2) 12b in response attaches to the mobile router 12a, and obtains from the mobile router 12a a sub-delegated prefix 32b having a value of “3:1:1::” and that is within the address space of the delegated prefix 32a “3:1::” assigned to the mobile router 12a. 
The mobile router 12b, having attached to the mobile router 12a, obtains a care-of address (CoA2) 36b based on the mobile network prefix 24a (based on the router advertisement message specifying the MNP 24a) and a care-of address (CoA1) 36c based on the delegated prefix 32a (based on the router advertisement message specifying the DP 32a). The mobile router 12b selects the care-of address 36c, performs a binding update to notify the home agent 14b of the care-of address 36c, and advertises its sub-delegated prefix 32b to the attached nodes 18 which in response establish their own respective care-of addresses 36d and 36e. Also note that the visiting mobile node attached to the mobile router 12b also builds a care-of address 36f (“2:1::9”) based on a router advertisement message from the mobile router 12b that specifies the MNP 24b. 
However, the prefix delegation by the mobile router 12a in FIG. 2 suffers from the disadvantage that restricting the sub-delegated prefix 32b to within the address space of the delegated prefix 32a of the mobile router 12a limits the flexibility by the mobile router 12b to move within the visited network 42 having the access router 26 as a point of attachment to the Internet 16. In particular, the prefix delegation by the mobile router 12a fails to provide inner mobility in the nested network topology 40 below the mobile router 12a: if any mobile router (e.g., 12a, 12b) changes its point of attachment within the visited network 42 provided by the access router 26, the mobile router must renumber all of its delegated prefixes.
Consider the example that mobile router 12b changes its attachment from the mobile router 12a to the access router 26: the mobile router 12b would need to discontinue use of the subdelegated prefix 32b because it conflicts with the delegated prefix 32a assigned to the mobile router 12a. Hence, the mobile router 12b would need to obtain a new delegated prefix (e.g., “3:2::”) from the access router 26. In addition, once the mobile router 12b determined that it was no longer attached to the mobile router 12a, the mobile router 12b would need to advertise its mobile network prefix 24b to maintain connectivity within its mobile network 30b, since the delegated prefixes 32a and 32b were no longer valid (reachable) prefixes. Hence, unknown visiting mobile nodes could build the care-of address 36f based on the MNP 24b, possibly revealing the identity of the mobile router 12b to an unknown visiting mobile node.
Moreover, assuming the mobile router 12a changed its attachment from the access router 26 to the mobile router 12b which is now attached to the access router 26, the mobile router 12a would need to discontinue use of its delegated prefix 32a because it is outside the address space of the new delegated prefix (“3:2::”) of the mobile router 12b. 
Further, the mobile routers 12a and 12b need to repeat the binding updates with their respective home agents 14a and 14b for each attachment because the prior delegated prefixes are no longer usable within the revised network topology.